This thesis consists of two distinct parts: Firstly, a core level spectroscopy study of SnS₂ and ternary oxide MgₓZn₁₋ₓO; secondly, the design and assembling of low electron energy diffraction instrument. In the former, the electronic structure and dynamics are investigated. In the study of the ternary oxide MgₓZn₁₋ₓO, the main goal was to better understand the influence of alloying MgO and ZnO as a method of bandgap engineering of ZnO. In the case of SnS₂, the focus of the investigation were the electronic properties of the material related to its layered structure as a source of both new fundamental physics and applications. The second part of the thesis describes the principles of design of the LEED instrument, its current functionality, operational instructions, and suggested further modifications for expanding its applications.

Societal challenges such as global warming and world poverty necessitate the development of alternative energy technologies which are independent of hydrocarbon combustion, utilize earth-abundant materials, and are inexpensive. Thus, in this Ph.D. dissertation, catalytic nanomaterials chemistry was employed to develop molybdenum(IV) sulfide (MoS2) as a device component in a variety of technologies including solar energy conversion, water-splitting, and energy storage. A simple, hydrothermal preparation was developed to grow MoS2 and MoSe2 ï¬lms directly from Mo foils, resulting in a petaled morphology that exposes a large number of catalytically active crystallite edge sites. Various characterization techniques indicated that the resulting multilayer MoS2 ï¬lms are frayed and exhibit single-layer MoS2 behavior at the edges. These self-supported electrodes also have an intermediate, MoSxOy layer. A synthetic approach to prepare MoSxOy-negative controls was also developed by growing petaled MoS2 on Au. Petaled MoS2 electrodes are highly active for the electrochemical reduction of aqueous polysulï¬de, demonstrating superior efï¬ciency in quantum dot sensitized solar cells compared to those employing Pt cathodes. The electrocatalytic hydrogen evolution reaction activity of petaled MoS2 and MoSxOy-negative controls are also compared. In addition to the equivalent chemical environment on the surface, we ï¬nd that petaled MoS2/Au and petaled MoS2/Mo exhibit comparable HER activity and kinetics. However, the exchange current density of petaled MoS2/Au is 3x smaller than that of petaled MoS2/Mo, being attributed to lower packing density on the Au support. Both petaled MoS2 ï¬lms have nearly ohmic contacts to their supports, demonstrating that MoSxOy is not resistive. Additionally, petaled MoS2 was evaluated in lithium ion batteries and it was found that the MoSxOy layer contributes greatly to the capacity of the electrode by promoting reversible Mo-MoO3 conversion, while other typical Li-S cycling intercalation reactions are not as prevalent. Ex situ characterization was utilized to elucidate the primary chemical species and reactions involved in the charge/discharge processes. Finally, Cu2S@SnS and SnS@Cu2S core@shell nanocubes prepared using a novel, rapid, cation exchange technique were evaluated as photoabsorbers in quantum dot sensitized solar cells.

Point-of-care diagnostics for malaria currently rely on antibody-based rapid diagnostic tests (RDTs), but these tests are in danger of becoming obsolete as the world moves to eliminate malaria. More sensitive and robust techniques are needed to detect lower parasite loads using a more diverse array of biomarkers. This work encompasses several strategies to improve low-resource malaria diagnostics. First, a fluorescent on-bead sandwich detection method for PfHRP2 was developed that relies on a robust, stable transition metal compound rather than enzyme-tagged antibodies to produce signal. Then, circular dichroism was used to determine that heme binding causes the protein rcPfHRP2 to adopt a more helical structure than its typical unstructured form. This shift in structure also adversely affects the proteinâs ability to bind to antibodies on RDTs and in ELISAs. Work then transitioned to focus on DNA-based diagnostics due to the valuable information that DNA biomarkers can provide, and the large unmet need for point of care DNA diagnostic tests. Initial work focused on simplifying the DNA extraction process into an automated format, which was then expanded to include PCR in-line with the extraction to eliminate operator steps. Finally, a DNA-based RDT was developed to detect a âbarcodeâ DNA sequence, as part of the bio-barcode assay. This assay amplifies target DNA by hybridizing the captured target to a gold nanoparticle tagged with hundreds of barcode DNA sequences. When the barcode sequences are released, the signal from one target DNA strand is amplified to a level detectable by the RDT. This particular bio-barcode assay has issues with nonspecific binding, so unfortunately the two aspects of this assay were never combined with good results. However, the DNA-based RDT could be used as a platform for future work to bring DNA-based malaria diagnostics to low-resource settings.

New Anionic Annulation Reactions and Anion Accelerated Amino-Cope Rearrangement. This dissertation compiles asymmetric anionic reactions of chiral Ellman sulfinyl imines and dienolates to access diverse nitrogen-containing compounds. Chiral sulfinimines and dienolates derived from 𝛾-bromocrotonates reacted diastereoselectively forming 3-pyrrolines and 𝑐𝑖𝑠-vinyl aziridines via a formal [3+2]-annulation and vinylogous 𝑎𝑧𝑎-Darzens reactions respectively. Concise asymmetric syntheses of three natural products have been achieved demonstrating the power of the [3+2]-methodology. Reaction of conjugated sulfinimines with enolates derived from non-halogen containing crotonates, were found to undergo a tandem diastereoselective α,α-addition, and anionic [3,3]-rearrangement affording vinylogous amide products. Synthesis of aromatic imines via 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) initiated oxidative aromatization highlights the synthetic value of the accelerated anion amino-Cope rearrangement.

This thesis describes the research conducted towards the overall goal of developing new synthetic organic methods to facilitate the synthesis of structurally complex nitrogen-containing polycyclic compounds. More specifically, I will describe the diverse reactivity of 1-aza-2-azoniaallene systems to make polycyclic diazenium salts and tetrahydropyridazine rings. I will also describe mechanistic studies undertaken to better understand this reactivity. The Brewer research group has discovered that hydrazones undergo an oxidation reaction with chlorodimethylsulfonium chloride to afford -chloroazo compounds, which react intramolecularly with pendent alkene units to give bicyclic ring fused and bridged diazenium salts. My work includes a mechanistic study to understand how the reaction proceeds and what factors affect its outcome. I will also describe the development of a new method to make diazenium salts in a shorter and more efficient route using a hypervalent Iodine (III) reagent. More recently, our group discovered new and different modes of reactivity of 1-aza-2-azoniaallene salts that included C-H amination reactions, polar [4 + 2] cycloadditions, electrophilic aromatic substitutions, and a chloroamination reaction. Our group was able to utilize these newly discovered reactivities in the preparation of pyrazolines, pyrazoles, tetrahydrocinnolines, and pyridazines, which are all complex compounds of great synthetic utilities that were made in short chemical transformations. Herein I describe my work to understand the scope and limitations of using these heteroallenes in the synthesis of pyridazines.

The need for a direct visual response system for the detection of organophosphorus compounds stems from the continued threat and use of these toxic agents in military and terrorist conflicts. The development of an enzyme-inhibitor triggered release system allows for direct visual detection with high specificity. Mesoporous silica nanoparticles (MSNs) have physical features that make them attractive as scaffolds for the construction of these systems, such as pore diameters (20-500 Á) that can be synthetically controlled, large surface areas (300-1500 m2g-1), large pore volumes, chemical inertness, stability at elevated temperatures, and surfaces that can be easily functionalized. In our studies, the dye Congo Red was loaded into the pores of MSNs, which were then capped by tethering an enzyme (organophosphorus hydrolase (OPH) or acetylcholinesterase (AChE)) to the external surfaces of MSNs through a competitive inhibitor (diethyl 4-aminobenzyl phosphonate (DEABP) or tacrine, respectively). OPH has been extensively studied for its ability to hydrolyze a wide range of organophosphorus compounds, rendering them non-toxic. AChE has been commonly used for organophosphate detection resulting from its sensitivity to phosphorylation. Upon addition of organophosphorus compounds to suspensions of the modified MSNs, the enzymes detached from the MSN surface, releasing the dye and providing a visual confirmation of organophosphate presence. Enzyme kinetics were studied using 31P NMR or UV-Visible spectroscopy; Congo Red release was also monitored by UV-Visible spectroscopy. The system was sensitive and specific for organophosphorus compounds both in phosphate-buffered saline and in human serum. The rate of dye release directly correlated with the rate of organophosphorus conversion for OPH and the rate of phosphorylation for AChE.

MhuD is a heme degrading enzyme from Mycobacterium tuberculosis that catalyzes both monooxygenation and dioxygenation leading to novel chromophores, mycobilins. The X-ray crystal structure of heme-bound, cyanide-inhibited MhuD displays a ruffled heme substrate where pyrrole rings are rotated around the Fe-N bonds, distorting the heme. The electronic structure of the heme in heme-bound, cyanide-inhibited MhuD (MhuD-heme-CN) is characterized here to provide insight into the mechanism of heme degradation by MhuD. Analysis of nuclear magnetic resonance (NMR) and magnetic circular dichroism (MCD) data for MhuD-heme-CN leads to the conclusion that the ground, (dxz,yz)4(dxy)1 electron configuration (2B2g state) and excited (dxy)2(dxz,yz)3 electron configuration (2Eg state) are close in energy allowing thermal population of the excited state at cryogenic and physiologically-relevant temperatures. The accessibility of two electronic states is studied with a combination of microbiology, spectroscopy, and computational analysis. The computational model developed describes a ground state that is close in energy to the excited state at ruffled geometries. Additionally, the heme is shown to be dynamic in the MhuD active site as the ground state hosts a double well potential in the ruffling coordinate allowing interconversion between a planar and a ruffled heme. To investigate the role of a ruffled, 2B2g heme and a planar, 2Eg heme in the MhuD reaction, substitutions are made to alter the active site residues Trp66 and Phe23. The Trp66 variants reduce heme ruffling resulting in decreased activity and a more planar heme as determined by optical spectroscopy and density functional theory calculations. F23W MhuD is shown to increase heme ruffling stabilizing the 2B2g state as determined by MCD. The F23W mutation stabilizes the meso hydroxyheme intermediate suggesting the more planar heme substrate conformation is needed to convert meso hydroxyheme into mycobilins. In summary, the data presented here strongly suggests that MhuD promotes formation of meso hydroxyheme with a ruffled substrate conformation and the formation of mycobilins with a more planar substrate conformation.

Cyclopentadienyl first row transition-metal compounds have been well studied since the 1950's, with the nearly ubiquitous CpFe(CO)2Me (FpMe) (Cp = η5-C5H5) being one of the first organometallics to be fully characterized. Despite the decades of study that have been poured into this complex, reactions between FpMe and primary phosphines have not been reported. Catalytic reactions with primary phosphines are generally understudied, including dehydrocoupling and P-C bond forming reactions such as hydrophosphination. A novel mechanism of dehydrocoupling and P-C bond formation that has received even more limited attention is α-elimination. This dissertation describes efforts in proving that FpMe is a competent catalyst for α-phosphinidene elimination through detailed trapping, labelling, and mechanistic studies. Additionally, the potential of α-elimination for the catalytic synthesis of phospholes from commercially available starting materials is shown, which is currently unknown. In the course of α-elimination studies, it was found that [CpFe(CO)2]2 (Fp2) is a visible-light activated photocatalyst for a variety of main-group bond forming reactions, including amine borane dehydrocoupling, siloxane formation, silylcyanation, and the double hydrophosphination of terminal alkynes with secondary phosphines. By utilizing commercially available and inexpensive LED bulbs Fp2 was an active catalyst for these reactions, which avoided the use of expensive, hazardous, and energy inefficient mercury arclamps. During studies to determine whether other cyclopentadienyl first row transition-metal compounds could catalyze α-elimination, it was found that CpCo(CO)I2 and Cp*Co(CO)I2 (Cp* = η5-C5Me5) are active catalysts for ammonia borane dehydrocoupling and transfer hydrogenation. These compounds are rare examples of cobalt compounds able to catalytically dehydrocouple amine boranes as well as catalyze a rare example of transfer hydrogenation that utilizes ammonia borane as a hydrogen source. I will also describe my year of research at Los Alamos National Laboratory (LANL) working under Dr. Jaqueline Kiplinger. Two primary projects are described herein: the first of which is the use of phenylsilane as a safe, versatile method for the synthesis of the bis(cyclopentadienyl) actinide hydrides [Cp*2An(H)(µ-H)]2 from the bis-alkyl complexes Cp*2AnMe2. It is shown that these hydrides are excellent precursors for the synthesis of a variety of actinide metallocenes. Additionally, in the case of uranium, by adjusting the equivalents of phenylsilane added, the oxidation state and nuclearity of the hydrides synthesized can be altered. Second, efforts in synthesizing a variety of novel actinacycles including actinacyclopentadienes, actinacyclocumulenes, a novel uranacyclopropene, and actinacyclopentadienecyclobutabenzenes that display alternating aromatic and antiaromatic character.

Electronic cigarette liquid (e-liquid) is a solution of propylene glycol and/or glycerol with varying concentrations of nicotine and flavorants. Inhalation of vaporized e-liquid is a method of nicotine delivery that is growing in popularity and is commonly regarded as safe relative to smoking traditional tobacco products. The thermal decomposition of glycerol and propylene glycol is typical of alcohols and has been investigated, although not exhaustively. In this work, samples of propylene glycol and glycerol were vaporized using an electronic cigarette (e-cigarette) and were analyzed for evidence of decomposition using nuclear magnetic resonance (NMR) spectroscopy. E-cigarettes are shown to degrade glycerol and propylene glycol into a diverse array of oxidation and dehydration products including glyceraldehyde, lactaldehyde, dihydroxyacetone, hydroxyacetone, glycidol, acrolein, propanal, acetone, allyl alcohol, acetic acid, acetaldehyde, formic acid, and formaldehyde. Evidence is presented that the abundance of these decomposition products may depend upon the temperature of the metal heating element but could also depend upon some catalytic aspect of the metal surface. The combination of formaldehyde with alcohols such as glycerol and propylene glycol was explored; hemiformals are stable hemiacetals that can be detected by NMR spectroscopy and are shown to be subject to hydrolysis when diluted in water. Investigations into smoking a glycerol-based tobacco mixture known as shisha using charcoals instead of metal heating elements also resulted in the dehydration of glycerol and sugars.

No description available.